Process of saturating fibrous conduits



Sept. 3, 1935. G EMBERG 2,012,961

PROCESS OF SATURATING FIBROUS CONDUITS Filed may 27, 1952 2 sheets-sheet1 lNvr-:NroR GEORGE EMBE/YG BY WMM ATTORNEY Sept. 3, 1935. G. EMBERGIvROCESS OF SATURATING FIBROUS CONDUITS Filed May 27, 1932 2Sheets-Sheet 2 mh VQ AI lNVENTOR @50H65 f/BERG ATTORNEY Cil PatentedSept. 3, 1935 UMTEDv STATES PROCESS OF SATURATING FIBROUS ND'UITS GeorgeEmberg, Chicago, Ill., assgnor to The Barrett Company, New York, N. Y.,a corporation of New Jersey Application May 27, 1932, Serial No. 613,937

s claims.

'I'his invention is directed to the saturation of absorbent products,and more particularly, to the saturation and impregnation of brousconduits employed to conduct and protect underground cables, telephonelines, electric light and other conductors and for the formation ofdrain pipes utilized for the discharge of corrosive liquids to renderthem substantially waterproof and resistant to abrasion, corrosion, andconditions encountered underground by brous conduits.

The brous bases of the conduits for the preferred embodiment of myinvention may be prepared in any Well known manner. For example,newsprint and paper pulp or other `fibrous material may be beaten in theusual paper beaters and the resultant stock screened and then pumped topaper cylinder machines and there formed into wet felts or paper. Thewet paper may be Wound about a cylindrical tube or mandrel to produce awet conduit of proper thickness. This conduit may be dried in kilns toremove the major portion of its moisture fc'ontent. The fibrous basemay, of course, be prepared in other known manner. Such conduits aremade in several sizes, varying from 2 inches to 6 inches or larger inexternal diameter, have an average wall thickness of approximately of aninch and are usually produced in 5, 6, and 8 foot lengths. The wallthickness of the conduits may, of course, be greater or less than 1%, ofan inch and other dimensions may vary. As they come from the dryingkilns, they usually contain from to 8 per cent moisture, althoughconsiderably more than 8 per cent moisture may, on occasion, be foundpresent.

The porosity or absorptive characteristics of the walls of fibrousconduits may vary within wide limits from a very dense wall of a densitycorresponding to hard wood and exceedingly difcult to saturate with lowcarbon water gas tar pitch or even with other waterproofing material,such as asphalt, to a porous open wall similar in density to that ofroofing felt, which will readily absorb bituminous saturants. Samples ofpresent commercial fibrous conduits have been tested and found to varyfrom substantially less than 1 cc. of voids per gram of tube wall to 2.8or more cc. of voids per gram of tube wall. To determine the cubiccentimeters of voids per gram of tube wall, a small sample of tube wall(say 2" x 5") is dried for one hour at 100 C., cooled, desiccated, andthereafter weighed. It is then immersed in kerosene, maintained at atemperature of 25 C., for 18 hours. Thereafter, the sample is removedfrom the kerosene, drained in vertical position for 30 seconds, andagain weighed. The difference in weight represents the keroseneabsorbed. This difference in weight in grams, divided by the specicgravity of the kerosene, corresponds to the cubic centimeters ofkerosene absorbed. This volume in cubic centimeters, divided by the (Cl.ill- 70) original weight in grams, gives the voids in cubic centimetersper gram.

The fibrous conduits, as they come from the drying kiln, containing from5 to 8 per cent of moisture, have heretofore commonly been impregnatedwith Water gas tar pitch by immersing them in tanks of molten pitchmaintained at atmospheric pressure or pressure above atmospheric and ata temperature of 300 F. or upwards. The conduits have in many cases beenallowed to soak in the molten pitch for from 'l to 12 hours, thenwithdrawn, and permitted to drain to remove excess saturant therefrom.

This process of saturating fibrous conduits, it will be noted, requiresthe soaking of the conduits for long periods of time to obtainsatisfactory penetration of the saturant throughout the walls of theconduit. In the practice of the process, numerous diiculties areencountered, among the most important of which may be mentioned- (1)Foaming of the pitch during the saturation of the conduits withconsequent loss of volatile oils from the pitch and restriction of theamount of pitch absorbed by the brous walls. This, I have found, maylargely be attributed to the moisture content of the fibrous tubes;

(2) Building up of the free carbon content of the pitch due to theprolonged maintenance of large bodies of pitch in which the conduits areimmersed under heat, resulting in decomposition of the pitch. Increasein the free carbon content of the pitch decreases the penetrability ofthe saturant and also results in carbon deposits on the walls of theconduit, preventing entrance of the saturant thereinto and resulting indefectively saturated conduits, i. e., conduits having white spotswithin the walls. The term free carbon is used in the sense common inthe coal tar industry to indicate material contained in the bituminoussaturant which is insoluble in benzol or carbon bisulde. It is commonlydetermined as described by Weiss (Journal of Industrial and EngineeringChemistry. vol. 10, 1918, pages 736 and 820, Test D5). It compriseshighmolecular carbon compounds of low solubility, carbon, and otherinsoluble material;

(3) Unsatisfactory saturation of the conduits due to the fibrous wallsnot absorbing sufficient saturant to render them substantiallywaterproof.

Conduits which are not adequately saturated do not attain maximumstrength and resistance to deflection or deformation; and

(4) In the case of saturation'of conduits under substantiallyatmospheric pressure, or under higher pressures, a substantial firehazard may exist. This is especially the case where increased pressureis produced by air pressure on the saturant and where incompletelycovered'and protected saturating tanks are used.

Water gas tar pitch has heretofore largely been employed as the saturantfor fibrous conduits. As is well known, water gas tar pitch is obtainedby distilling tar derived from carburetted water gas made by enrichingblue gas with products of pyrogenic decomposition of petroleum oils. Theoils constitute the chief source of tar present in the carburetted watergas. Water gas tar pitch is, therefore,'essentia1ly of petroleum originand it is recognized that water gas tar pitch differs materially incomposition from other pitches, particularly coal tar pitches derivedfrom the distillation of tar obtained from coal distillation gases.Water gas tar pitch has been employed for saturating fibrous conduitslargely because of its relatively low free carbon content (about 2 to 7per cent) its improved waterproofing properties as compared withasphalt; and its capability to protect the fibrous base against moldsand fungi. employed forv thesaturationof'V conduits, generally speaking,they are less satisfactory than pitch in that they are less waterproofand do not effectively withstand and protect against molds and fungi andother cellulose destroying organisms. V

In order to satisfactorily protect cables and other electricalconductors, it is important that the conduit besubstantially'waterprocf, resistant to abrasion and soil pressures, andcapable of withstanding underground conditions and not punctured orbroken by the soil anddebris,v surj- A rounding it. v'One ofthetests-to.which-conduits are subjectedtodetermine theirV Waterproofnessis to immerse them indistil'led water, maintained at a temperature ofapproximately 7721i. forlr'4 hours, then ascertain",thepercentagevincrease in# the weight of the conduit-and thus arrive at'the amount ofwater absorbed thereby. VPresent cona temperature of approximately '77F., will absorb not more than 6 per cent moisture represents asatisfactory waterproof conduit; a conduit absorbing not more than 4 percent moisture under these conditions is regarded as eminentlysatisfactory. It should be noted that as indicated hereinabove, many ofthe saturated fibrous conduits now made, when subjected to thewaterproofness test briefly described above, show an absorption ofmoisture substantially in excess of 4 per cent,- many of them absorbing12 per cent and more moisture. In general, the lower the waterabsorption, the more satisfactory is the product.

It is an object of the present invention to provide a process of makinga saturated fibrous conduit in which the voids are substantiallycompletely filled with saturant, and which upon immersion in `distilledwater for 48 hours at a temperature of 77 F. will absorb substantiallyless than 4 per cent moisture. A further object is to provide a processof making fibrous conduits which are more resistant to corrosion, todeflecv tion and deformation stresses, `to abrasion, and to soilpressures than known conduits, and the Walls of which are of greatertensile strength than those of known conduits. It is another object ofthis invention to provide a process of saturating fibrous conduits whichpermits the employment of coal tar pitch as the saturant. Other objectsand advantages of this invention will appear from the following detaileddescription.

In the impregnation of porous articles with bi- Whilein somecasesasphalts have been tuminous saturant, two of the factors which tend toprevent satisfactory saturation are- 1. Air in the pores or voids, and

2. Moisture on the fibers .or other solid surfaces and as vapor in thepores.

Air and water vapor in the pores of the material tend to prevententrance of the saturant, and water on the material surfaces tends toprevent wetting of the surfaces by the saturant.

When saturation is attempted at atmospheric pressure, the major portionof the water may be removed by long soaking in the hot saturant at atemperature above the boiling point of water. The escaping steam carrieswith it some air. The removal of water by this means is time-consumingand air is not completely removed. By the heretofore commonly practicedmethods of saturation, therefore, the voids of the saturated article areincompletely filled with saturant.

If it is attempted to improve the degree of saturation lby applyingpressure, some improvement is found, but saturation is still imperfect.The effect of pressure is, by forcing additional saturantl into thematerial, to compress residual air and water vapor in the pores, even tothe extent of somewhat compressing, densifying, and deforming the wallsof the saturated article. On release of pressure, the compressed air andwater vapor expand, forcing pitch out from the material` therebyreducing the -degree of saturation `evenfdistribution of the saturant.'My"finvntion largely or entirely eliminates Y these disadvantages andproduces an article the voids 'ofwhich are nearly or completely filledvwith saturant. Such articles are more resistant to water-absorption,abrasion, deflection. and deformation. In`the process of my invention,the wallsof thev brous conduits are not subjected to pressure or otherconditions which would ca use densication or compression of the tubeWalls with consequent increased resistance to absorption of saturant,but on the contrary the pores or` voids are evacuated, materiallyincreasing the absorbing capacity of the tube wall.

In accordance with this invention, the conduits are first dried. yThisis preferably accomplished by placing them in a basket'in a container.The container is then heated and subjected to vacuum,` which maypreferably be of the order of from 17 to 29 inches of mercury and may bemaintained for from a few minutes to two hours or more, depending uponthe amount of water, the structure of the conduit walls, etc. Thus,substantially all moisture and occluded air and other gas are removedfrom the conduit walls. Molten waterproofing saturant, preferably of abituminous nature, is then progressively introduced into the containeruntil the conduits are completely immersed. Maintenance of the vacuum onthe conduits during the gradual addition of the bituminous saturantpermits the saturant to enter the evacuated voids or pores immediatelyupon contact with the walls of the conduit; prior removal of themoisture and air precludes foaming. Hence, thorough saturation of thevconduit readily takes place and the conduit walls absorb considerablymore saturant than is possible with other methods of saturation orimpregnation. After the conduit is completely immersed in the saturant,the vacuum may be interrupted and the conduits permitted to soak for aslong as 45 minutes or longer.

In my preferred procedure of drying, I subject the conduits to besaturated to a vacuum gradually increasing to a maximum, say 28 to 29inches of mercury, and hold them at this vacuum while heating them longenough to remove substantially all water, water vapor, and air from thevoids, without allowing them to contact with the pitch saturant. Whenthus dehydrated and deaerated, I permit pitch to come into contact withthem. Even while the pressure head on any given point of the tube due tothe level of pitch in the tank is low, the capillarity of the porcscauses a considerable amount of pitch to be absorbed. Increase ofpressure head of the pitch forces additional amounts int-o the vaporandir-free voids, effecting substantially complete saturation.

Slow increase of head of pitch has the added advantage of permittingsatisfactory saturation with saturants containing fine suspended matterl* like the free carbon of coal tar pitch. Slow increase in pressure (asis well known in the filtering art) tends to eliminate the building upof impenetrable layers of such suspended matter (e. g. free carbon) onthe surface of the fiber conduit, and by eliminating such layers,assures greater penetration and improved saturation.

The higher the vacuum attained, the more effective is the removal of airand water from the voids and the more complete is the absorption ofsaturant.

I have discovered that coal tar pitch, preferably a pitch having amelting point cf from 140 to 180 F., can in accordance with the processoi this invention, be employed as the saturant. Pitch of a melting pointas high as 225 F. may be employed in special cases, e. g. with conduitshaving large 4size voids. Preferred pitches having melting points offrom 140 to 180 F. or higher will have a free carbon content of from 5to 9 per cent, but pitches of higher free carbon content up to from 15to 25 per cent, or even higher may be used to give commerciallysatisfactory saturation under favorable conditions, e. g., in saturatingproducts having unusually open structure.

Preferably coa-l tar pitch made by a Vacuum distillation process, suchfor example as disclosed in Patent No. 1,759,816, granted May 20, 1930,or other processes minimizing decomposition of the tar undergoingdistillation, is employed as the saturant. Pitches made by a lowtemperature vacuum distillation process are characterized by low freecarbon content and I have found that such pitches are particularlysuitable as the saturant for fibrous conduits. For example, such a pitchof 149 F. melting point (water bath) had a free carbon content of from 5to 9 per cent; such pitch of 158 F. melting point (water bath) had afree carbon content of from 5 to 9 per cent; such pitch of 226 F.melting point (air bath) had a free carbon content of from 1l to 15 percent; and such kpitch of 291 F. melting point (air bath) had a ffreecarbon content of from 16 to 21 per cent.

Pitches produced by distilling tar not under vacuum but by continuouslyheating the tar and then passing the heated tar into a vapor box wherethe vapors separate from the pitch have considerably higher free carboncontents for the same melting point pitch, e. g., pitch proof 149 F.(water bath) had a free carbon content of from 11 to 13 per cent; apitch of 158 F. melting point (water bath), had a free carbon content offrom 10 to 14 per cent; a pitch of 226 F. (air bath) had a free carboncontent of from 19 to 23 per cent; and a pitch of 291 F. melting pointhad a free carbon content of from 33 to 37 per cent. The free carboncontent will depend largely on the melting point of the pitch and thefree carbon content of the tar used to make the pitch. Coke oven targenerally will not run much above 5 per cent free carbon 1 per cent freecaroon content is very low fo-r such tars.

The use of a pitch made by a vacuum distillation process for saturationhas a two-fold advantage:

(1) In its manufacture, this pitch is distilled under vacuum andconsequently'at a lower temperature than would be needed to produce apitch of the same melting point by the usual methods of distillation.This low temperature causes minimum decomposition and hence minimum freecarbon formation in the pitch. Low free carbon content is an aid ineffecting complete penetration and saturation of porous material.

(2) In its manufacture, the pitch has been subjected to temperature andvacuum conditions such as to insure the substantially complete removalof oils which would be volatile under the conditions maintained in thesaturating operation of my invention. Such pitches will be sub- In thepreferred embodiment, illustrated on the drawings, the invention isshown incorporated in the production of a fibrous conduit saturated witha bituminous saturant and the present disclosure will be confined to thepresent illustrated embodiment of the invention. It will be understood,however, that the novel features and improvements are susceptible toother applications, such. for example, as the saturation of absorbent.products generally. Included in the scope of my invention is thesaturation of conduits, piping and other conductors made of cement,concrete, cement-asbestos mixture, or other porous materials capable ofbeing saturated with waterproofing compounds. The conduits produced bymy process are net only resistant to external pressures, such as soilpressures, but by suitable choice of materials and saturatingconditions, may be made resistant to high internal pressures and hencesuitable for pipe lines conveying corrosive Waters or the like. Hence,the scope of this invention is not confined to the improvement hereindescribed.

In the drawings, Fig. 1 is a side elevation, paltly in section,illustrating the apparatus for saturating conduits; and

Fig. 2 is a side elevation of a modified arrangement of apparatus forsaturating conduits.

In the drawings, Fig. 1, reference numeral I indicates a saturating tankor container, preferably of an over-all height of approximately 5 feetin excess of the length of the conduits or tubes to be treated. A cover2 has a flange 3 arranged to be bolted or otherwise secured againstvacuum leakage, as indicated at 4, to flange 5 on container I. In lieuof bolting the cover to the container, flanges 3 and 5 may be ground toform a gas tight joint when properly assembled. Cover 2 has a hook oreye 6 to permit ready removal from and placement onto the tank I.

The bottom of the container is shown provided with a steam jacket 1having steam inlet 8 and outlet 9 for supplying heat to the tank I,although other heating means may be employed. At a point near the baseof the container, a screen or other suitable support II is provided fora basket I2 containing the conduits I3 to be impregnated. Heatinsulating material (not shown) may be disposed about the tank and otherparts 'of the apparatus to reduce heat losses therefrom.

Saturant is supplied to the tank I through valve-controlled pipe I4,disposed at the base of the tank. An overow pipe I5 is connected to aside wall of the tank near the top thereof. This pipe may communicatewith a storage tank (not shown) for the saturant. Extending through theside of tank I, through a gas-tight packed joint, is a pipe I6. 'I'hispipe is communicably connected with condenser I1 having inlet I8 andexit I9 for cooling water or other medium. A suction pump 2l of anysuitable type is connected by pipe 22 with the trap 26 into which leadssection 23 of pipe I 6. A baffle 28 in the trap 26 prevents flow ofliquid through the trap into the vacuum line 22. Pipe 24 connects trap26 with oil and water collector 25. Valves 21 are disposedin pipe linesI6, 22, and 24 to control ow therethrough.

In the arrangement of apparatus shown in Fig. 2, 3| indicates a meltingkettle which may be suitably heat insulated. Burners 32 are providedbeneath the kettle to heat the contents thereof. Kettle 3| communicateswith saturating tank 40 bymeans of pipes 34, 35 having valves 36, 31therein, pipe 35 leading into the base of the vertical tank 46. Avalve-controlled discharge pipe 38 communicates with pipe 35 and leadsto a storage tank (not shown) or other point of disposal of residualpitch in saturating tank 40. The tank 40, as indicated on the drawings,is of a relatively great height and is provided with suitable supportsfor basket 33 containing the fibrous conduits to be saturated.

Tank 40 may be heated directly by burners 39 disposed about its sidesand base or may be steam heated, e. g., by steam coils. Gaseous orliquid fuel may be fed to these burners. Cover 4I seals the top of thetank. In Fig. 2, the cover is shown as bolted to the tank, asindicatedby reference numeral 42, a gasket being inserted between thecover and flange of the tank to give a gas-tight joint. Athermometer-well 43 is formed in the top of the cover. Ports 44 and 45are formed in the sides of the saturating tanks. Port 44 com- .municatesby means of pipe 46 vwith a mercury barometer 41 or other pressureindicating device to show the vacuum in the saturating container. Theother port 45 is connected through pipe 48 with a receptacle 49,permitting visual inspection of any distillate which may come over fromthe saturating tank 40. A valve-controlled drain pipe 58 leads fromreceptacle 49 permitting removal of the contents of the receptacle.

Pipe 5I connects the receptacle 49 with a safety tank 52. This tankfunctions to collect any foam coming from the saturating tank andprevents the entrance of this foam into the vacuum line. Discharge ofthe contents of tank 52 may be effected through valve-controlled pipe53. A mercury barometer 54 or other pressure indicating devicecommunicates by means of pipe 55 with the safety tank 52.Valve-controlled pipe 56 connects tank 52 with the vacuum pump 51.

In operation, the fibrous conduits to be saturated are placed in aperforated basket, preferably though not necessarily in verticalposition, and the basket then inserted in the saturating tank, beingsupported therein somewhat above the base of the tank. As indicated inFigs. 1 and 2, the tanks are of an over-al1 height such that aconsiderable open space is provided above the top of the conduits.Thereafter, the cover is suitably sealed onto the saturating tank. Thevacuum pump is started and the container or saturating tank heatedsimultaneously with the generation of the vacuum. 1n the case of theapparatus of Fig. 1, this is accomplished by passing steam through thejacket 1. In the apparatus of Fig. 2, the container is heated by directilre from burners 39. Preferably before heating the container, saturantis admitted thereto to a level just below the bottom of the tubes asindicated by the line 6I on Fig. 1. 'Ihe saturant in the base of thecontainer prevents destruction of the container walls during the heatingthereof to drive out the moisture and occluded gas from the fibrousconduits and prevents over-heating of the fibrous conduits.

A vacuum of from 1'7 to 29 inches of mercury, preferably about 27 inchesof mercury, may be maintained during the 'drying of the conduits,although lower vacuum may, of course, be employed. The heating of theconduits under vacuum is carried on until substantially all moisture andoccluded gas are removed therefrom. Just how long this should takedepends upon the porosity of the conduit, their initial moisturecontent, etc. For a fibrous conduit having about 1.6 cc. of voids pergram of tube wall and containing a moisture content of approximately 5to 6 per cent, heating for from 45 minutes to 2 hours should suiilce.The optimum temperature in the container or saturating tank during thedrying of the conduit will depend upon the percentage of Water, size ofvoids, density of the material, time cycle, and other factors. In onecase, 140 F. was found to be satisfactory with a vacuum of 27 inches ofmercury when drying conduits containing approximately from 5 to 8 percent moisture and having 1.6 cc. voids per gram of tube wall.

After the moisture and occluded gas'have been removed, the saturant isgradually added through pipe I4 (Fig. 1) 'or through pipes 34 and 31(Fig. 2) while the vacuum is maintained on the fibrous conduits.Utilizing coal tar pitch having a melting point of about 158 F., havinga ""rree carbon content of about 6 per cent, and a specific gravity ofabout 1.23 at C., the pitch is maintained in tlzi saturating kettle at atemperature of about 3 F.

In the case oi.' the apparatus of Fig. 2, the flow of the saturant iscontrolled by regulating valve 31, the suction on the container causingthe saturant to gradually rise thereinto. The rate of flow of thesaturant into the container or tank and the vacuum maintained thereinmay be controlled so that a substantially constant suction is maintainedon the saturant as it rises in the tank. Flow into the apparatus of Fig.1 is controlled by manipulation of the valve in line I4 or regulatingthe speed of the pump communicating with pipe I4. This flow may be soregulated that it takes from 15 minutes to an hour for the saturant torise to a level above the tops of the conduits, indicated by` the line62 in Fig. 1.

Thereafter, the vacuum may be interrupted, or if desired maintainedwhile the brous conduits soak in the saturant. The period of soaking inthe case of less dense tubes or conduits may be varied from 45 minutesto 2 hours; a longer period may be required for more dense tubes. Duringentrance of the saturant into the tanks, the vacuum pump may be operatedto maintain a substantially constant suction on the conduit Walls, thuspermitting the saturant to enter the evacuated pores or voids andprevent reentry of air or other gas thereinto or the vacuum may beallowed to decrease to a greater or less degree as the saturant isintroduced.

If the vacuum has not been released upon the completion of the entry ofthe saturant into the tank, it is released at the end of the soakingperiod, the cover removed, and the basket of saturated tubes or conduitstaken out of the tank. The vacuum may be gradually released so thatpressure gradually increases on the body of saturant forcing additionalsaturant into the fibrous tubes. 'I'hey may then be allowed to drain forfrom 2 to 6 minutes or longer, cooled, and stored for shipment to theconsumer. If desired, the conduits, prior to finaly draining, may begiven a wash treatment with bituminous saturant at a temperature higherthan that of the saturant to remove any foreign matter, such as lint,adhering to the saturated tube Walls.

The pitchy remaining in the tank 33 (Fig. 2) by opening valves 36 and 31is permitted to return to kettle 3| disposed at a level below that ofthe base of tank 33 as shown in Fig. 2. If desired, the pitch remainingin the tank 33 may be drained to a tank or other point of disposalthrough pipe 38 by keeping valve 36 closed and opening valve 31 and thevalve in pipe 38. Vapor coming oi from the saturant in the case of theapparatus of Fig. 1 is condensed in condenser I1 and the condensatecollected in the oil and water collector 25. Any oils coming off fromthe pitch may be separated from the water in the collector 25 andreturned to the system. In the apparatus of Fig. 2, liquid collected inreceiver 49 and safety tank 52 may be conserved.

In the drawings, I have shown tubes or conduits treated in a verticalposition. By suitable changes in the apparatus, I may treat them equallyeffectively in a horizontal position.

In the table below there are given three examples of processes ofsaturating fibrous tubes, having about 1.6 cc. of voids per gram of.tube wall and approximately 7 per cent moisture, in accordance with thisinvention.

Example number I II III Weight of unsaturated tube-. 1.740 kg--- 1.790kg 1.785 kg. Weight of saturated tube---.. 5.730 kg--- 5.750 kg--- 5.450kg Weight of pitch saturant ab- 3.990 kg..- 3.960 kg-.- 3.665 kg scrbedby the tube. Percentage saturation.-.-. 220395.--- 221 .2%-- 205.6%.Vacuum in inches of Hg mam- 27 inches-- 27 inches-- 27 inches tained onsaturating tank during initial drying period. Duration of dryingperiod..-. nun.-- 45 mln. 60 min Temperature of pitch in melt 320 F. 320F- 320 F ing kettle. Time required for tiow of l5 m1n- 30 sec 60 nungitch from storage tank or ettle to saturating tank after drying wascompleted. Total time vacuum was exmm--- 45% mm-. 120 min.

erted on fibrous conduits. Time of soaking conduits in 120 mm---45mm---- 60 mm.

saturant. Temperature of saturant in 320 F- 320 F 320" F.

which the conduits were u ts.

In each of the above examples 8 inches of pitch were placed in thebottom of the saturating tanks during the vacuum drying. The pitch waskept hot by steam heating the saturant, and the vapors coming over werecondensed and collected.

Sections through the top, middle, and bottom of the saturated conduitsof Example II were tested for waterproofness, i. e., were immersed indistilled water at a temperature of about '10 F. for 48 hours and thefollowing results obtained:

Section Top Middle Bottom Weight after test Weight before test Weight ofH20 absorbed. Percentage absorption..

537.2 grams.. 521.6 grains.. 15.6 grams.-- 3.05%

564.7 grams.. 552.0 grams.- 12.7 grams... 2.30%

620.0 grams. 616.0 grams. 4.0 grams. 0.65%.

It will be noted that the average percentage absorption of the threesections representing the percentage absorption of the conduit is 2 percent.

I have found, as a result of work performed, that a conduit having about1.6 cc. of voids per gram of tube wall saturated in accordance with myinvention with coal tar pitch will absorb an amount of saturant equal tomore than 200 per cent of the weight ofthe dry unsaturated base. In thecase of Examples I and II above, it will be noted that the conduitabsorbed approximately 225 per cent by weight of saturant. In saturatingvery dense fibrous conduits, for example, conduits having approximately0.67 cc. of voids per gram of tube wall, with coal tar pitch or otherbituminous saturant, the amount of saturant absorbed will be found to beat least 80 per cent by weight of the dry unsaturated base.

Instead of drying the conduits in the preferred manner by subjectingthem to vacuum as hereinabove described, the conduits may be soaked inhot saturant, such as coal tar pitch or other bituminous waterproofsaturant, until foaming of the pitch stops and substantially allmoisture is removed from the conduit walls. The saturant is maintainedat a temperature materially above the boiling point of water during thedrying of the conduits, for example, at a temperature of about 300 F.If. this procedure is followed, present equipment for saturating brousconduits involving the soaking of the conduits in the hot saturant maybe employed to dry the conduit. After the conduits have been dried, theymay be saturated under vacuum in accordance with this invention. Thesaturant employed may be the saturant in which the conduits wereimmersed to elect the drying or fresh waterproong saturant may beutilized.

It will be noted that the process of this invention results in a morethorough saturation of the fibrous conduits than prior processes andrequires materially less time for efficient saturation and impregnationof the fibrous conduits. The conduit of this invention has the voids orpores substantially completely filled with coal tar pitch or othersaturant employed and has the coal tar pitch or other saturant coveringthe fibers and bonding with the pitch in the voids. Hence, the brousbase is eiectively waterproofed and protected against corrosion,abrasion, and soil pressures. In prior conduits, the voids are notcompletely lled with the saturant as in the conduit of this invention;prior conduits, therefore, are distinctly less waterproof than are theconduits of my invention. Further, in prior saturated brous conduits,probably due to the long time immersion of the bases in the hotsaturant, the

ltendency for charring and burning of the organic bases of the conduitssaturated in accordance with this invention is substantially eliminatedsince the time of contact between the organic bases and the saturant ismaterially reduced.

As the saturant for the practice of the preferred embodiment of thisinvention, coal tar pitch, preferably at a temperature of from 300 to330 F., is employed; this results in a product of substantially improvedcharacter. The conduit of this invention, saturated with coal tar pitch,absorbs materially less moisture, is more resistant to corrosion,abrasion and soil pressures, and is of greater tensile and compressivestrength than the saturated conduits heretofore known to me. It is alsomuch more resistant to attack by molds, fungi, and allcellulose-destroying organisms. Further, conduits saturated with coaltar pitch have strikingly improved waterproofness. The conduits of theinvention have been immersed for 48 hours in distilled water at ateniperature of '77 F. and have absorbed substantially less than 4 percent water, and as little as about l per cent water. As among coal tarpitches, I prefer to use those produced by a vacuum or other lowtemperature process, having a relatively low "free carbon content, andundergoing relatively little volatilization loss under the conditions ofmy saturating process.

Itis to be understood that this invention is not restricted to thepresent disclosure otherwise than defined by the appended claims.

I claim:

1.`The process of saturating conduits having relatively rigid walls ofsubstantial thickness and density and constituted of organic fibrousmaterial with a bituminous saturant in heat liquefied condition andwhich saturant upon prolonger contact with the conduits at saturatingteniperatures would cause substantial thermal deterioration of the wallsth-ereof,`whieh comprises subjecting the conduits to heat and vacuumeonditions to remove cccluded gas therefrom, thereafter, whilemaintaining the conduits under vacuum, gradually immersing them in thebituminous saturant maintained in heat liquefied condition at anelevated temperature so that the saturant enters and fills the voids andentry of air into the voids is prevented, and then soaking the conduitsin the saturant for a period of time insuiiicient to cause substantialthermal deterioration of the conduit walls but sufiicient to impregnatethe conduits so that when immersed in distilled Water at '17 F. for 48hours they will absorb less than 4 per cent water.

2. The process of saturating dense paper eonduits having relativelyrigid walls of substantial thickness with a bituminous saturant in heatliquefied condition and which saturant upon prolonged contact with theconduits at saturating temperatures would cause substantial thermaldeterioration of the walls thereof, which comprises subjecting theconduits to heat and vacuum conditions to remove cccluded gas therefrom,thereafter, while maintaining the conduits under vacuum, graduallyimmersing them in the time insuiiicient to cause substantial thermaldeterioration of the conduit walls but sufficient to impregnato theconduits so that when immersed in distilled water at 77 F. for 48hoursthey will absorb less than 4 per cent water.

-3. The process of saturating conduits having relatively rigid walls ofsubstantial thickness and density and constituted of organic fibrousmaterial with a coal tar pitch saturant containing free carbon, whichcomprises subjecting the conduits to heat and vacuum conditions out ofcontact with the saturant to remove cccluded gas therefrom andthereafter, while maintaining the conduits under vacuum, graduallyimmersing them in the said coal tar pitch saturant, whereby theformation of an impenetrable layer of free carbon on the surface of thefibrous conduits is prevented and the saturant enters and fills thevoids and entry of air into the voids is prevented.

4. The process of saturating conduits having relatively rigid walls ofsubstantial thickness and density and constituted of organic fibrousmaterial with a coal tar pitch saturant containing free carbon, whichcomprises subjecting the conduits to neat and vacuum conditions out ofcontact with the saturant to remove occluded gas therefrom, thereafter,while maintaining the conduits under vacuum, gradually immersing them inthe said coal tar pitch saturant whereby the formation of animpenetrable layer of free carbon on the surface of the fibrous conduitsis prevented and the saturant enters and fills the voids and entry ofair into the voids is prevented and then soaking the conduits vin thecoal tar pitch saturant for not more than two hours.

5. The process of saturating conduits having relatively rigid walls ofsubstantial thickness and density and constituted of organic fibrousmaterial with a bituminous saturant containing free carbon andmaintained in heat liquefied condition at an elevated temperature, whichcomprises immersing dry conduits in the saturant while maintainingvacuum conditions in the saturating zone so as to prevent the formationof an impenetrable layer of free carbon on the surface of the conduitsand thereafter permitting the conduits to soak in the hot saturant for aperiod of time insufficient to cause substantal thermal deterioration ofthe fibrous base of the conduits but sufficient to substantiallycompletely fill the voids in the walls of said conduits.

6. The process of saturating conduits having relatively rigid walls ofsubstantial thickness and density and constituted of organic fibrousmaterial with a bituminous saturant maintained in heat-liquefiedcondition at an elevated temperature and which saturant upon prolongedcontact with the conduits at saturating temperatures would causesubstantial thermal deterioration of the walls thereof, which comprisessubjecting the conduits to heat and vacuum conditions to remove occludedgas, immersing the conduits 1n the saturant, maintaining vacuumconditions in the saturating zone while the conduits are immersed in thesaturant and permitting the c/onduits to soak in the hot saturant for aperiod of time insufficient to cause substantial thermal deteriorationof the fibrous base of the conduits but u water.

GEORGE EMBERG.

A CERTIFICATE 0F CORRECTION.

Patent No. 2,012,961. September 3, 1935.

GEORGE EMBERG.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 3,firat column, after line 68, insert the syllable and words duced inlthis manner having a melting point; and page 6, first column, line 40,claim 1, for "prolonger" read prolonged; and that the said LettersPatent shouldberead with these corrections therein that the same mayconform to the record of the Acase in the Patent Office.

Signed and sealed this 8th day of October, A. D. 1935.

l Leslie Frazer (Seal) 'Acting Commissioner of Patents.

